Stepping motor



momjOm R. H. HALL STEPPING MOTOR mm ON hm VN Filed July 5, 1960 A ril 23, 1963 Richard H. Hall,

INVENTOR.

BY ../J2 f ATTORNEY.

United rates The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to stepping motors and particularly to electrical stepping motor having improved characteristics.

The principal difiiculty with presently known stepping motors is their speed limitation. A second is the difiicnlty and complexity by which bidirectional rotation is achieved.

Accordingly, the objects of the present invention are to increase stepping speed substantially and to provide at the same time a simple means of changing the direction of stepping rotation.

In accordance with the invention a stepping motor is constructed in which a ratchet wheel is driven by pawls attached to each end of a balanced rocker arm pivoted about an axis vertically above and parallel to the axis of the ratchet wheel. The rocker arm is driven by electromagnetic coils positioned in a balanced fashion with respect to and magnetically acting upon the rocker arm. Special spring means are incorporated to both zero-return the rocker arm and provide a detent for locking the ratchet wheel when the rocker arm is in a zero or neutral position.

This invention will be more clearly understood by referring to the accompanying drawing in which:

FIGURE 1 is a plan view of an embodiment of the invention;

FIGURE 2 is an enlarged sectional view along plane 22 of FIGURE 1; and

FIGURE 3 is a sectional view along plane 3-3 of FIGURE 1.

Referring first to FIGURE 2, rocker arm 10, having pawis 12 and 14 connected to each end of the rocker arm, is pivoted on shaft 16 just above shaft 18 which supports ratchet wheel 20. Pawls l2 and 14 partially engage ratchet wheel teeth on both sides of the wheel (left and right on the drawing), as illustrated, when the rocker arm is in a neutral, zero, or unenergized, position. These pawls, which bend to the outside (left pawl to left and right pawl to right) when they are acted on by rocker arm 10, under the influence of electromagnets 28 and 28a or 30 and 30a, to rotate ratchet wheel 20, must have a stiffness under compression, but flexibility to the side. As an example, pawls made of fiat spring steel .005 inch thick spot welded to a laminated soft iron rocker arm may be employed for the pawl-rocker arm assembly. Combined return or zero position spring-ratchet wheel detent 22 is held fast by mounting 23 symmetrically positioned between the spring ends, which ends engage, in a neutral position, teeth on the ratchet wheel to provide a bidirectional detent or looking action. Spring 22, which symmetrically slants down to said ends to contact wheel 20, also engages rocker arm at intermediate points 25 and 27 to provide a neutral return force to rocker arm 10. Electromagnets 28, 28a, 30 and 30a, as shown in FIGURE 1, are positioned respectively under each corner portion of rocker arm 10 and provide the force to actuate the rocker arm. The coils of these electromagnets are connected through single pole-double throw switch 32 to a source 31 of positive pulses. Electromagnets 28 and 28a are positioned under two mt nice 3,087,077 Patented Apr. 23, 1963 corner portions on opposite face sides of ratchet wheel 20 to act on one end of rocker arm 10 and coils 30 and 30a are positioned under the other two corner portions on opposite face sides of ratchet wheel 20 to act on the other end of rocker arm 10. As shown in FIG- URE 3, the lower ends of coil cores 34 of electromagnets 28 and 28a are magnetically coupled by permeable member 36. Similarly the lower ends of coil cores 34 of electromagnets 30 and 30a are magnetically coupled by an identical permeable member which is not shown. The shaft 18 of ratchet wheel 20 is supported by bearings 38 and 40 mounted in motor case 42 (FIGURE 3). Shafts 43 and 45 support rocker arm 10 in bearings 46 and 48 positioned at opposite ends of case 42.

To examine the operation of the stepping motor assume that it is desired to step the ratchet wheel 20 in a counterclockwise direction. Coils 28 and 28a act in unison on one side of the rocker arm when energized by a pulse from source 31 through single pole, double throw switch 32 to pull down that side (left side in FIGURE 2) of the rocker arm. Lowering of the rocker arm on the left side, under the influence of coils 28 and 28a, causes pawl 12 to act in a counterclockwise direction on ratchet wheel 20 and to lift the detent portion 29 (on right side of spring) of spring 22 and pawl 14 out of engagement with ratchet wheel 20 so that the ratchet wheel may respond and step around in a counterclockwise direction. At the termination of the pulse, and thus termination of the downward force by electromagnets 23 and 28a on rocker arm 10, rocker arm 10 rises back to a neutral position under the restoring force of spring 22. The downward travel of rocker arm 10- is determined by the clearance between rocker arm 10 and coil cores 34, and thus determines the size of the steps. By the same return motion the right side detent portion 29 of spring 22 returns to engagement with ratchet wheel 20 and provides counterclockwise locking force on the ratchet wheel. Clockwise lock is achieved by virtue of the engagement of the left detent portion 31 of spring 22 with the next tooth of ratchet wheel 20. This prevents backlash as pawl 12 slides upward over the teeth of ratchet wheel 20 as rocker arm 10 returns to a neutral position.

Clockwise stepping of ratchet wheel 20 is similarly achieved when switch 32 is repositioned to apply pulses to coils 30 and 30a.

Stepping motors constructed in accordance with the foregoing invention have achieved stepping speeds in either direction of steps for second, far in excess of known stepping motors.

It can be seen that this device has many variations and applications which do not depart from the spirit of the invention. Therefore it is desired that the following claims not be restricted by the specific examples set forth in the specification.

Therefore what is claimed as new and is desired to be secured by Letters Patent of the United States is:

1. A bidirectional stepping motor comprising a ratchet wheel positioned to turn on a first axis, a balanced rocker arm pivoted centrally on a second axis vertically above and parallel to said first axis, first and second pawls connected, respectively, to opposite ends of said rocker arm and extending vertically downward to engage teeth of said ratchet wheel so as to step the ratchet wheel in a clockwise or counter clockwise direction, a spring arm supported centrally above said axes, the ends of said spring arm being adapted to engage between teeth of said ratchet wheel when in a balanced position, and intermediate points between said ends of said spring arm and the point of said central support engaging opposite arm sides of said rocker arm for applying a neutralizing force to said rocker arm, first and second electromagnetic means positioned respectively adjacent and directly below each end of said rocker arm for selectively forcing downward said rocker arm ends whereby the movement of said rocker arm is substantially parallel to the magnetic pull of said electromagnets.

2. The stepping motor set forth in claim 1 wherein each of said first and second electromagnetic means comprises first and second electromagnets positioned, respectively, on each face side of said ratchet wheel and said rocker arm comprises permeable surfaces adjacent upper core ends of said electromagnets, and a permeable member magnetically linking the lower ends of the cores of said electromagnets.

4 3. The stepping motor set forth in claim 2 further comprising a source of electrical pulses, and switching means connected to said source and said first and second electromagnetic means for selectively applying electrical pulses to either said first or second electromagnetic means.

References Cited in the file of this patent UNITED STATES PATENTS 1,022,742 Kellum Apr. 9, 1912 1,061,624 Moore May 13, 1913 2,490,013 Bramley Dec. 6, 1949 

1. A BIDIRECTIONAL STEPPING MOTOR COMPRISING A RATCHET WHEEL POSITIONED TO TURN ON A FIRST AXIS, A BALANCED ROCKER ARM PIVOTED CENTRALLY ON A SECOND AXIS VERTICALLY ABOVE AND PARALLEL TO SAID FIRST AXIS, FIRST AND SECOND PAWLS CONNECTED, RESPECTIVELY, TO OPPOSITE ENDS OF SAID ROCKER ARM AND EXTENDING VERTICALLY DOWNWARD TO ENGAGE TEETH OF SAID RATCHET WHEEL SO AS TO STEP THE RATCHET WHEEL IN A CLOCKWISE OR COUNTER CLOCKWISE DIRECTION, A SPRING ARM SUPPORTED CENTRALLY ABOVE SAID AXES, THE ENDS OF SAID SPRING ARM BEING ADAPTED TO ENGAGE BETWEEN TEETH OF SAID RATCHET WHEEL WHEN IN A BALANCED POSITION, AND INTERMEDIATE POINTS BETWEEN SAID ENDS OF SAID SPRING ARM AND THE POINT OF SAID CENTRAL SUPPORT ENGAGING OPPOSITE ARM SIDES OF SAID ROCKER ARM FOR APPLYING A NEUTRALIZING FORCE TO SAID ROCKER ARM, FIRST AND SECOND ELECTROMAGNETIC MEANS POSITIONED RESPECTIVELY ADJACENT AND DIRECTLY BELOW EACH END OF SAID ROCKER ARM FOR SELECTIVELY FORCING DOWNWARD SAID ROCKER ARM ENDS WHEREBY THE MOVEMENT OF SAID ROCKER ARM IS SUBSTANTIALLY PARALLEL TO THE MAGNETIC PULL OF SAID ELECTROMAGNETS. 